High pressure pump

ABSTRACT

A pump assembly includes a housing, and first and second rotor that are rotatable within the housing and mesh with each other. The pump assembly includes wear plates arranged on opposing sides of the rotors and a separation mechanism that is engageable with the wear plates and enables axial movement of the wear plates relative to the rotors. The wear plates are normally biased to be disengaged from the rotors and axially moveable to engage the rotors when pressure in the pump assembly exceeds a predetermined pressure threshold. The rotors may be lobe gears that each include a plurality of lobes. The lobes may include wiper retaining recesses that retain wiper inserts and the walls of the wiper retaining recesses may have pressure trapping grooves that enable trapped fluid to flow out of the wiper retaining recesses for pressure relief.

FIELD OF INVENTION

The present invention relates generally to a positive displacement pump, such as a rotary lobe gear pump that is suitable for pumping large amounts of low viscosity fluid at high speed.

BACKGROUND

Positive displacement pumps may generally be used in high pressure applications for pumping large amounts of fluid, such as oil and gas refining, offshore drilling, transportation refueling, aircraft refueling, mining, and chemical processing. Different types of positive displacement pumps may be suitable for use in particular high pressure applications. Positive displacement pumps such as gear pumps may have pressure compensating plates such as wear plates or thrust plates that are pushed against the face of a gear during high pressure operation of the pump. However, the wear plates may remain in contact with the gear when the pump is operating at a lower pressure and friction causes the wear plates to gall up and seize up the gears after a short dry run period. Thus, conventional pumps that use normal pressure compensating plates may be unable to continuously dry run at lower pressures such that conventional pumps are unable to efficiently operate at both high pressures and low pressures.

SUMMARY OF INVENTION

The present invention provides a high pressure pump assembly having enhanced performance as compared to conventional configurations. A lobe gear pump is shown and described herein, but the principles described herein may be implemented in any suitable type of positive displacement pumps. The high pressure pump may be a gear pump having externally toothed gears. In exemplary embodiments, the pump assembly has spring-biased plastic wear plates that are normally disengaged from the metallic rotors (or gears) and axially moveable to engage the rotors when pressure in the pump assembly exceeds a predetermined pressure threshold. Using the spring-biased wear plates enables the pump assembly to both operate at high pressures during which the wear plates are engaged with the gears and low pressures during which the wear plates are disengaged from the gears. During the high pressure operation of the pump, the fluid in the pump chamber will be channeled to a cavity behind the wear plates. Once pressure increases beyond the threshold point, the high pressure fluid compresses the springs to bring the wear plates closer to the gear. A minimal gap between the gears and the wear plates ensures that there is no leakage of fluid to the low pressure inlet side of the pump. On the other side of the pump, during the low pressure operation or during the dry run of the pump, the springs will disengage the wear plates and push the wear plates apart from the gear. The gap between the components will ensure a wear-free smooth functioning of the pump during a dry condition. Thus, the pump may continuously dry run without causing wear on the gears of the pump.

The rotors may be lobe gears that each have a plurality of lobes and the present invention may provide further pressure compensation by using pressure trapping grooves formed in wiper-retaining recesses of the lobes. During operation of the pump, the pressure trapping grooves help in relieving the high pressure trapped underneath the wiper blades while the wiper blades are travelling back and forth inside the wiper retaining recesses (or slots). During the operation, the wiper blade of one of the lobes retracts into the wiper retaining recess when the wiper blade comes in contact with another lobe or the pump chamber interior surface. During this motion, high pressure fluid which is trapped inside the wiper retaining recess may be without an escape path and cause damage to the lobe gear or wiper blades. The pressure trapping grooves help the trapped fluid to escape outside of the wiper retaining recess into the pump chamber and thus enable a smooth functioning of the pump.

According to one aspect of the invention, a pump assembly includes a housing and a first rotor and a second rotor that are rotatable within the housing and mesh with each other, and a plurality of wear plates including a first wear plate arranged on a first side of the rotors and a second wear plate arranged on a second side of the rotors opposite the first side. The pump assembly includes a separation mechanism that is engageable with the plurality of wear plates to enable axial movement of the plurality of wear plates relative to the rotors, such that the plurality of wear plates are normally disengaged from the rotors and axially moveable to engage the rotors when pressure in the pump assembly exceeds a predetermined pressure threshold.

According to another aspect of the invention, a pump assembly includes a first rotor and a second rotor that are each rotatable about a longitudinal rotor axis. Each rotor has a plurality of lobes that each has a longitudinal lobe axis that is parallel with the rotor axis. The rotors mesh upon rotation without contacting each other and a plurality of wiper retaining recesses, or slots defined in each of the plurality of lobes. Each lobe includes a longitudinally extending base and opposing walls that extend radially outwardly from the longitudinally extending base to define the wiper retaining recess. Each of the opposing walls has a plurality of pressure trapping grooves that are defined in the opposing walls and extend radially outwardly and are open to the periphery of the lobe gear. The pump assembly includes a plurality of wiper inserts associated with each of the plurality of lobes and retained within the plurality of wiper retaining recesses. Each wiper insert is depressibly radially biased outward from the lobe of the rotor such that the wiper can contact the at least one of the other rotor and the interior chamber of the first housing upon rotation of the rotors.

According to another aspect of the invention, a pump assembly includes a drive motor rotatably driving a first drive shaft in a first direction or a second direction, a first timing gear mounted on and coupled to the first drive shaft, a second timing gear driven by the first timing gear and mounted on and coupled to a second driven shaft, and a first rotor and a second rotor. Each rotor has a plurality of lobes and the first rotor and second rotor are rotatable without contacting each other. The first rotor is mounted on and coupled to the first drive shaft and the second rotor is mounted on and coupled to the second driven shaft. The pump assembly includes a lobe gear pump housing having an interior chamber in which the first rotor and second rotor are rotatable, a plurality of wear plates including a first wear plate arranged on a first side of the plurality of lobes and a second wear plate arranged on a second side of the plurality of lobes opposite the first side, and a separation mechanism that is engageable with the plurality of wear plates to enable axial movement of the plurality of wear plates relative to the plurality of lobes. The plurality of wear plates are normally disengaged from the plurality of lobes and axially moveable to engage the plurality of lobes when pressure in the lobe gear pump housing exceeds a predetermined pressure threshold.

The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the pump assembly according to the present invention.

FIG. 2 is another perspective view of the pump assembly of FIG. 1.

FIG. 3 is a sectional view of the pump assembly of FIG. 1.

FIG. 4A is a detailed section view of the pump assembly of FIG. 3 showing a position of wear plates of the pump assembly during a low pressure (dry run) operation of the pump assembly.

FIG. 4B is a detailed section view of the pump assembly of FIG. 3 showing a position of the wear plates during a high pressure (wet run) operation of the pump assembly.

FIG. 5 is an exploded perspective view of the pump assembly of FIG. 1.

FIG. 6 is a detailed sectional view of the pump assembly of FIG. 1 showing the lobe gears.

FIG. 7 is a perspective view of one of the lobe gears shown in FIG. 5.

FIG. 8 is a perspective view of another embodiment of a lobe gear according to the present invention.

DETAILED DESCRIPTION

The principles of the present invention may be suitable for use with pump assemblies used in high pressure and dry run applications. The principles may have particular application to a gear pump assembly. The pump assembly described herein may be suitable to provide pumping for stationary, mobile, and high vapor-pressure fluid applications. Examples of suitable applications may include oil and gas refining, offshore drilling, transportation refueling, aircraft refueling, mining, and chemical processing. The pump assembly is shown and described as a lobe gear pump assembly, but the principles described herein are not limited to a lobe gear pump assembly and may be used in any suitable pump. For example, the pump assembly may be a gear pump including rotors having externally toothed gears. An exemplary lobe gear pump assembly is described in International Patent Application Publication Number WO 2017/066091, of which the entirety is hereby incorporated herein by reference.

Referring first to FIGS. 1-5, a pump assembly 10 is shown and the pump assembly 10 may be a lobe gear pump assembly. The lobe gear pump assembly may be a fixed displacement pump. The pump assembly 10 may include a lobe gear pump 12 and a centrifugal pump 14. The lobe gear pump 12 may include a first housing or a lobe gear housing 18 having an interior chamber 20 (shown in FIGS. 3 and 5), an inlet 21 (shown in FIG. 5), and an outlet 22. The outlet 22 or discharge interface may include a bolt or a flange-type interface 24.

The lobe gear pump 12 may further include a first rotor 26 and a second rotor 28 (shown in FIGS. 3 and 5) rotatably housed within the interior chamber 20 of the lobe gear housing 18. The pump assembly 10 may further include a drive motor 32 shown herein as an AC motor, but any suitable drive motor such as a hydraulic motor or DC motor may be employed. A suitable motor may have approximately between 60 and 80 horsepower. The drive motor 32 may drive a first drive shaft 34 which counter rotatingly drives a second driven shaft 36 through a pair of timing gears 38, 40 each mounted on a respective shaft 34, 36 (shown in FIGS. 3 and 5). The first drive shaft 34 may be directly driven by the drive motor 32 such that no speed reduction gearing is used. The timing gears 38, 40 may be herringbone gears that have a high contact ratio and are housed in a timing gear housing 42. The timing gear housing 42 is secured to the housing of the drive motor 32 on one end and secured to at least one center plate 39 on the other end thereof. The timing gears 38, 40 may be made of any suitable material such as an alloy steel. The timing gears 38, 40 may lie within an oil bath in the timing gear housing 42 to operate quietly and efficiently.

The first rotor 26 may be mounted on the first drive shaft 34 and the second rotor 28 may be mounted on the second driven shaft 36. The first drive shaft 34 and the second driven shaft 36 may extend through the center plate 39 to engage the timing gears 38, 40. The center plate 39 may engage with the timing gear housing 42 and against the lobe gear housing 18 when assembled. The first drive shaft 34 and the second driven shaft 36 may be rotationally supported on either side of the rotors 26, 28 by bearings 43 (shown in FIG. 3). The drive motor 32 creates torque and speed, which is transferred by the timing gears 38, 40. The timing gears 38, 40 provide the torque for the rotors 26, 28 as well as provide timing between the rotors 26, 28.

Referring in addition to FIGS. 5-8, each rotor 26, 28 may have a lobe gear configuration such that each rotor 26, 28 includes a plurality of lobes 30 (shown in FIGS. 5-8). In a gear pump assembly, each rotor 26, 28 may have a plurality of external teeth such that the rotors 26, 28 mesh with each other during rotation. In a lobe gear pump assembly, each lobe 30 of the rotors 26, 28 mesh with each other while the rotors 26, 28 counter rotate but do not make contact with each other due to the timing gears 38, 40. In the lobe gear assembly, each rotor 26, 28 may include four lobes 30, as shown in FIG. 5-7, or three lobes 30, as shown in FIG. 8. Any suitable number of lobes may be used and any suitable material may be used. For example, the lobe gears may be formed of aluminum.

As best shown in FIGS. 3-5, the pump assembly 10 may also include a plurality of pressure compensating plates such as thrust plates or wear plates. The plurality of pressure compensating plates may be a plurality of wear plates 44 that are mounted adjacent the rotors 26, 28. In a gear pump assembly, the rotors 26, 28 may be toothed gears. In a lobe gear configuration of the rotors 26, 28, the wear plates 44 may be mounted adjacent the corresponding lobes 30. The plurality of wear plates 44 may include at least one first wear plate 44 a arranged on a first side 30 a of the rotors 26, 28 and at least one second wear plate 44 b arranged on a second side 30 b of the rotors 26, 28. The wear plates 44 a, 44 b may extend generally perpendicular to the axis of rotation of the rotors 26, 28. Accordingly, the rotors 26, 28, or the lobe gear may be interposed or sandwiched between the first wear plate 44 a and the second wear plate 44 b. The wear plates 44 a, 44 b may be made of plastic material and the lobe gears may be made of metallic material. In another embodiment, the wear plates 44 a, 44 b may be made of metallic material and the lobe gears may be made of metallic material with plastic material overmolded to the ends of the lobe gears to avoid metal-to-metal contact.

The pump assembly 10 may also include a separation mechanism 45 that is engageable with the plurality of wear plates 44 to enable axial movement of the plurality of wear plates 44 relative to the plurality of lobes 30. The separation mechanism 45 may include at least one pre-loaded spring 45 a that normally biases the plurality of wear plates 44 towards a first position, as shown in FIG. 4A, in which the plurality of wear plates 44 are disengaged from the lobe gear or the plurality of lobes 30. Each wear plate 44 may have a side face 44 c that engages against a side face of the rotors 26, 28 or gears. The rotors 26, 28 may have a first side face on the first side 30 a and a second side face on the second side 30 b of the rotors 26, 28. Each side face of the rotors 26, 28 may contact a side face 44 c of a corresponding wear plate 44.

The wear plates 44 may have any suitable shape. An example of a suitable shape is a cylindrical shape, or an oval cylinder shape. As best shown in FIG. 5, the wear plates 44 may have apertures 44 d for receiving the drive shafts 34, 36 therethrough. The apertures 44 d may be defined in the side face 44 c of the wear plate 44. The wear plates 44 may have an axially extending shoulder 44 e that extends from the side face 44 c. The axially extending shoulder 44 e may receive at least one o-ring 45 b or a plurality of o-rings. The wear plates 44 may include a retaining surface 44 f on the periphery of the side face 44 c for retaining a plurality of o-rings 45 c.

The separation mechanism 45 may include a first set of pre-loaded springs 45 a associated with the first wear plate 44 a and a second set of pre-loaded springs 45 a associated with the second wear plate 44 b. When pressure in the pump assembly exceeds a predetermined pressure threshold, the pressure will be large enough to overcome the spring force of the pre-loaded springs and the plurality of wear plates 44 will axially move to a second position, as shown in FIG. 4B, in which the plurality of wear plates 44 are engaged against the plurality of lobes 30. Any suitable type of spring may be used. The separation mechanism 45 is shown and described as a spring, but other biasing mechanisms may be suitable for use with the wear plates.

Using the wear plates 44 and the separation mechanism 45 enables the pump assembly 10 to be dry runnable by way of the running clearance between the wear plates 44 and the plurality of lobes 30 being kept at a predetermined distance via the separation mechanism 45. During the dry run, as shown in FIG. 4A, no contact force may be exerted from the wear plate 44 to the lobe gear such that the pump assembly 10 can dry run at lower pressures for a long period of time without heating up the contact surface between the components. When the wear plates are engaged with the lobe gears during high pressure operation (or wet run), as shown in FIG. 4B, the pump assembly 10 may be operable at high fluid pressures of up to around 500 pounds per square inch. Thus, the dry running clearance (FIG. 4A) that is maintained during low pressure operation is greater than the wet running clearance (FIG. 4B) that is maintained during high pressure operation.

As best shown in FIGS. 6-8, the rotors 26, 28 may include a plurality of wiper inserts or wiper blades 46 located on each lobe 30 that are designed to create a seal within the interior chamber 20 of the lobe gear housing 18 (shown in FIGS. 2 and 3). The wiper blades 46 may prevent fluid leak through the gaps in between the lobes 30 and between a lobe 30 and walls 19 of the interior chamber 20. The wiper blades 46 may be manufactured from any suitable material such as a filled PEEK material that is both self-lubricating and durable. The wiper blades 46 may contact the walls 19 of the interior chamber 20 and the opposite rotor 26, 28. Thus, the wiper blades 46 may be durable enough to contact the rotors 26, 28 but also have self-lubricating properties so as not to create wear which allows the pump assembly 10 to be continuously dry run without damaging the pump.

With reference to FIG. 8, the rotors 26, 28 may have a body 47 formed of a suitable metallic material such as aluminum. The ends 47 a of the body 47 may be overmolded with an engineering plastic, such as PEEK, and machined to form ends 47 b of the rotors 26, 28. During operation of the pump assembly 10, the rotors 26, 28 are positioned and timed so that the metallic rotor profiles do not touch each other, and nor do they contact or rub against the lobe gear housing 18. The ends 47 b of the rotors 26, 28 do contact or rub against the lobe gear housing 18. The engineering plastic ends 47 a may act as wear plates on both sides of the rotors 26, 28 to avoid metal to metal contact. Using the plastic ends 47 a may further enable the pump assembly 10 to dry run without causing wear on the components.

The wiper blades 46 may include longitudinally extending apertures 46 a across the wiper blade 46 to promote further lubrication. The apertures 46 a may allow lubricant to fill the apertures 46 a and improve surface interaction to reduce the wear on the wiper blade 46. The wiper blade 46 may be biased outwardly from the lobes 30 by at least one spring 48 that keeps the wiper blade 46 in contact with the pump chamber walls 19 or the surface of a meshing lobe 30 to prevent leakage. More than one spring 48 may be used per wiper blade 46. Each wiper blade 46 and corresponding springs 48 may be retained within a wiper retaining recess 49 defined within each lobe 30. The springs 48 allow the wiper blades 46 to move radially back and forth within the wiper retaining recesses 49 such that at least one wiper blade 46 will be in contact with the other lobe gear and the interior chamber 18 during rotation. Each lobe 30 may include any suitable number of wiper retaining recesses 49 and wiper blades 46. For example, each lobe 30 may include three wiper retaining recesses 49 and wiper blades 46 (shown in FIG. 8) or four wiper retaining recesses 49 and wiper blades 46 (shown in FIGS. 6 and 7). Each lobe 30 may have a longitudinal axis that is parallel with a longitudinal axis of the corresponding rotor 26, 28 and the wiper retaining recesses 49 may extend longitudinally in a direction that is parallel to the longitudinal axis of each lobe 30. Each wiper retaining recess 49 may be located at an outermost location of the respective lobe 30. The lobe 30 may include a longitudinally extending base 49 a and opposing walls 49 b, 49 c that extend perpendicularly from the longitudinally extending base to define the wiper retaining recess 49 between the opposing walls 49 b, 49 c for retaining the wiper blades 46.

During meshing of the rotating lobe gears, dead volume between the wiper blades 46 and the lobes 30 may be compressed to cause increased pressure within the wiper retaining recesses 49. The lobe gear may include a plurality of pressure trapping grooves 50 for pressure relief in the wiper retaining recesses 49. Each pressure trapping groove 50 may be defined in each of the opposing walls 49 b, 49 c. The plurality of pressure trapping grooves 50 may include a first set of pressure trapping grooves 50 a that are defined in the first wall 49 b and a second set of pressure trapping grooves 50 b that are defined in the second wall 49 c. The first set of pressure trapping grooves 50 a and the second set of pressure trapping grooves 50 b may be facing one another and both the first set of pressure trapping grooves 50 a and the second set of pressure trapping grooves 50 b enable fluid flow out of the wiper retaining recess 49. Any suitable number of pressure trapping grooves 50 may be used and the pressure trapping grooves 50 may be evenly spaced along each of the opposing walls 49 b, 49 c. The pressure trapping grooves 50 may extend perpendicularly to the longitudinally extending base 49 a. During operation of the pump assembly 10, the pressure trapping grooves 50 help in relieving the high pressure trapped underneath the wiper blades 46 during the back and forth motion of the wiper blades 46 inside the wiper retaining recesses (or slots) 49. During the operation, the wiper blade 46 of one of the lobes 30 retracts into the wiper retaining recess 49 when it comes in contact with another lobe 30 or the pump chamber interior surface. During this motion, high pressure fluid which is trapped inside the wiper retaining recess 49 may be unable to escape and cause damage to the lobe gear or wiper blades 46. The pressure trapping grooves 50 provided in the wiper retaining recesses 49 help the trapped fluid to escape outside into the pump chamber 20 and thus enable a smooth functioning of the pump assembly 10.

The wiper blade 46 may be shaped as an inverted “T”. The springs 48 may be formed as an “X-spring” from any suitable material such as a tempered or hardened stainless spring steel. The springs 48 may be formed from a continuous band having a pair of arms 51 extending from a base portion 52 of the spring and crossing each other generally at a midpoint of each arm such that the arms form an “X”. Each of the pair of arms of the wiper blade spring 48 has a portion which is generally half the width of the base portion 52 of the spring 48. The ends 53 of each of the pair of arms 51 of the wiper blade spring 50 are generally the same width of the base portion 52 of the spring 48. The configuration of the wiper insert spring 48 provides stability and prevent rocking back and forth such as in conventionally used leaf springs. The spring 48 may enable pressure to be distributed evenly along the base portion 52. The springs 48 may be inserted into slots 54 in a base portion of the wiper blade 46 to help retain the spring in the corresponding rotor 26, 28.

Referring again to FIGS. 1-5, the centrifugal pump 14 of the pump assembly 10 may include a second housing (also referred to as a centrifugal pump housing) 55 attached to the lobe gear housing 18 and having an inlet 56 and an outlet 58. The inlet 56 may include an inlet cover having a first inlet flange interface 59 a and a second inlet flange interface 59 b having a greater diameter than the diameter of the first inlet flange interface 59 a. The outlet 58 of the centrifugal pump housing 55 may be connected to the inlet 21 of the lobe gear housing 18 by a fluid connecting member 60 shown as an elbow flange. It should be recognized that the pump assembly 10 may be reversible and that in such a case the outlet 22 may act as an inlet and the inlet 56 may act as an outlet. The centrifugal pump housing 55 may also include a seal-on-nose or an inlet seal 61 having an o-ring.

The pump assembly 10 may include an impeller 62 (shown in FIGS. 3 and 5) that is rotatably positioned in a shrouded portion of the centrifugal pump housing 55 and is mounted on and is rotationally driven by the drive shaft 34. The impeller 62 may be made of any suitable material such as stainless steel which is durable and has the capability of handling vapor bubbles. The impeller blades may be preferably optimized to be sharp, large, and smoothly machined to allow for faster acceleration of the fluid during rotation of the impeller 62. The impeller 62 may be shrouded and allow for a quick acceleration of the fluid from the leading edge to the blade. The rotating impeller 62 may act as a centrifugal pump to pump fluid into the inlet 21 of the lobe gear housing 18. The rotation of the impeller 62 transfers energy from the drive motor 32 to the fluid being pumped by accelerating the fluid onwards from the center of rotation through the volute impeller outlet, i.e. the outlet 58 of the centrifugal pump housing 55 and the fluid connecting member 60 to the inlet 21 of the lobe gear housing 18. This results in the ability of the impeller 62 to establish the pressure boost to the rotors 26, 28 to pump more flow without resulting in cavitation. The use of the impeller 62 may eliminate the need for a speed reduction gearbox by allowing the pump assembly 10 to run at high speeds (1800+ rpm) to generate higher flow than in conventional lobe gear pumps.

During operation of the pump assembly 10 in a typical application of fluid transport, fluid is taken in from a tank or hose through the inlet 56 to the centrifugal pump 14 and given an inlet pressure boost via rotation of the impeller 62 as driven by the drive motor 32 through the first drive shaft 34. The fluid is collected in the impeller volute and rerouted to the lobe gear housing 18 via fluid connecting member 60. The fluid, having a boost of inlet pressure, is then pumped through the lobe gear rotors 26, 28 and enters a high volume cavity in the interior chamber 20 of the lobe gear housing 18 and is pumped outward through the outlet 22 of the lobe gear housing 18 to discharge into the system.

During operation, the heat from the drive motor 32 and the heat generated from the timing gears 38, 40 may significantly elevate the temperature within the timing gear housing 42. In order to help cool the timing gear housing 42, the timing gear housing 42 may have external cooling fins 66 and an internal cooling chamber 68 (shown in FIGS. 1, 2 and 5). A portion of the fluid being pumped by the lobe gear pump may be redirected from the outlet 22 to the internal cooling chamber 68 where heat is transferred to the fluid which flows from the internal cooling chamber 68 back to the inlet 21 of the lobe gear housing 18. The timing gear housing 42 may include a conduit 70 for transferring fluid back to the inlet 21 of the lobe gear housing 18. The cooling fins 66 and cooling channel 68 may enable fast heat dissipation and increase the life of bearings, timing gears, and seals in the pump assembly 10. The pump assembly 10 may also optionally include a thermal management system housed in a junction box 72 attached to the drive motor 32. An exemplary thermal management system is described in International Patent Application Publication Number WO 2017/066091 and incorporated herein by reference.

The high pressure pump assembly described herein provides an advantage over conventional pump assemblies in that the pump assembly described herein enables the pump to operate at both high pressures and low pressures. Disengaging the wear plates from the lobe gears during a low pressure or dry run operation improves the life of the pump assembly by preventing wear on the rotating components. The pump assembly also enables maintaining a tight running clearance between the lobe gears and the wear plates.

A pump assembly may include a first rotor and a second rotor that each are rotatably mounted in the housing and meshing with the other rotor. The pump assembly may include a plurality of wear plates including a first wear plate arranged on a first side of the rotors and a second wear plate arranged on a second side of the rotors opposite the first side, and a separation mechanism that is engageable with the plurality of wear plates to enable axial movement of the plurality of wear plates relative to the rotors. The plurality of wear plates may be normally disengaged from the rotors and axially moveable to engage the rotors when pressure in the pump assembly exceeds a predetermined pressure threshold.

The separation mechanism may include at least one pre-loaded spring associated with each of the first wear plate and the second wear plate.

The plurality of wear plates may have a first position in which the plurality of wear plates are disengaged from the rotors and a second position in which the plurality of wear plates are engaged against the rotors. The plurality of wear plates may be biased towards the first position and moveable from the first position towards the second position.

The first rotor and the second rotor may be formed of a metal material and the plurality of wear plates may be formed of a plastic material.

The rotors may be externally toothed gears.

The rotors may be lobe gears that each have a plurality of lobes and the housing may be a lobe gear pump housing in which the rotors are rotatable without contacting each other.

The pump assembly may include a centrifugal pump housing that is attached and fluidly connected to the lobe gear pump housing and has an interior chamber, and an impeller that is arranged within the interior chamber centrifugal pump housing and rotatable within the interior chamber. The impeller may be configured to pressurize fluid and direct the fluid to the lobe gear pump housing. The plurality of wear plates may axially move to engage the plurality of lobes when pressure in the lobe gear pump housing exceeds a predetermined pressure threshold.

The pump assembly may include a plurality of wiper inserts and each wiper insert may be interconnected to one of the plurality of lobes of each of the first rotor and the second rotor. Each wiper insert may be depressibly radially biased outward from the lobe of the respective rotor such that the wiper insert can contact the other of the first rotor and the second rotor and the interior chamber of the lobe gear pump housing upon rotation of the first rotor and the second rotor.

Each of the plurality of lobes may include a plurality of wiper retaining recesses and each wiper retaining recess may be located at an outermost location of a respective lobe. The respective lobe may include a longitudinally extending base and opposing walls extending perpendicularly from the longitudinally extending base to define the wiper retaining recess therebetween for retaining the wiper insert.

The pump assembly may include a plurality of pressure trapping grooves defined in each of the opposing walls of the respective lobe.

The plurality of pressure trapping grooves may include a first set of pressure trapping grooves defined in a first wall of the opposing walls and a second set of pressure trapping grooves defined in a second wall of the opposing walls. The first set of pressure trapping grooves may face the second set of pressure trapping grooves and both set of pressure trapping grooves enable fluid flow out of the wiper retaining recess.

The pressure trapping grooves may be evenly spaced along each of the opposing walls.

A pump assembly may include a first rotor and a second rotor that are each rotatable about a longitudinal rotor axis and each rotor may have a plurality of lobes that each have a longitudinal lobe axis that is parallel with the rotor axis. The first and second rotor may mesh upon rotation without contacting each other. A plurality of wiper retaining recesses may be defined in each of the plurality of lobes. Each lobe may include a longitudinally extending base and opposing walls that extend radially outwardly from the longitudinally extending base to define the wiper retaining recess. Each of the opposing walls have a plurality of pressure trapping grooves that are defined in the opposing walls and extend radially outwardly for pressure relief in the plurality of wiper retaining recesses. The pump assembly may include a plurality of wiper inserts associated with each of the plurality of lobes and retained within the plurality of wiper retaining recesses. Each wiper insert may be depressibly radially biased outward from the lobe of the rotor such that the wiper can contact the at least one of the other rotor and the interior chamber of the first housing upon rotation of the rotors.

The plurality of pressure trapping grooves may include a first set of pressure trapping grooves defined in a first wall of the opposing walls and a second set of pressure trapping grooves defined in a second wall of the opposing walls. The first set of pressure trapping grooves may face the second set of pressure trapping grooves. Both sets of pressure trapping grooves enable fluid flow out of the wiper retaining recess.

The pressure trapping grooves may be evenly spaced along each of the opposing walls.

The pump assembly may include at least one wiper spring that biases the wiper insert radially outwardly. The wiper spring may be retained within the wiper retaining recess.

The pump assembly may include a first housing having an interior chamber and the first rotor and second rotor may be rotatable within the interior chamber of the first housing. The pump assembly may include a second housing that is attached to the first housing and has an interior chamber. The second housing may be fluidly connected to the first housing. The pump assembly may include an impeller that is rotatable within the interior chamber of the second housing.

The pump assembly may include a first drive shaft and the first rotor may be mounted on and coupled to the first drive shaft. The pump assembly may include a first timing gear mounted on and coupled to the first drive shaft and a second timing gear driven by the first timing gear and mounted on and coupled to a second driven shaft. The second rotor may be mounted on and coupled to the second drive shaft. The pump assembly may include a drive motor rotatably driving the first shaft in a first direction or a second direction and the impeller may be configured to pressurize fluid and direct the fluid to the inlet of the first housing when the drive motor is rotating the first drive shaft in the first direction.

A pump assembly may include a drive motor rotatably driving a first drive shaft in a first direction or a second direction, a first timing gear mounted on and coupled to the first drive shaft, a second timing gear driven by the first timing gear and mounted on and coupled to a second driven shaft, and a first rotor and a second rotor that each have a plurality of lobes. The first rotor and the second rotor may be rotatable without contacting each other with the first rotor being mounted on and coupled to the first drive shaft and the second rotor being mounted on and coupled to the second drive shaft. The pump assembly may include a lobe gear pump housing having an interior chamber in which the first rotor and second rotor are rotatable, a plurality of wear plates including a first wear plate arranged on a first side of the plurality of lobes and a second wear plate arranged on a second side of the plurality of lobes opposite the first side, and a separation mechanism that is engageable with the plurality of wear plates to enable axial movement of the plurality of wear plates relative to the plurality of lobes. The plurality of wear plates may be normally disengaged from the plurality of lobes and axially moveable to engage the plurality of lobes when pressure in the lobe gear pump housing exceeds a predetermined pressure threshold.

The pump assembly may include a plurality of wiper retaining recesses defined by walls of each of the plurality of lobes. Each of the plurality of wiper retaining recesses may have a plurality of pressure trapping grooves that are defined in the walls to enable pressure relief within the plurality of wiper retaining recesses. A plurality of wiper inserts may be associated with each of the plurality of lobes and retained within the plurality of wiper retaining recesses.

The pump assembly may include a centrifugal pump housing that is attached and fluidly connected to the lobe gear pump housing and has an interior chamber, and an impeller that is arranged within the interior chamber centrifugal pump housing and rotatable within the interior chamber. The impeller may be configured to pressurize fluid and direct the fluid to the lobe gear pump housing.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

1. A pump assembly comprising: a housing; a first rotor and a second rotor, each rotor rotatably mounted in the housing and meshing with the other rotor; a plurality of wear plates including a first wear plate arranged on a first side of the rotors and a second wear plate arranged on a second side of the rotors opposite the first side; and a separation mechanism that is engageable with the plurality of wear plates to enable axial movement of the plurality of wear plates relative to the rotors, the plurality of wear plates being normally disengaged from the rotors and axially moveable to engage the rotors when pressure in the pump assembly exceeds a predetermined pressure threshold.
 2. The pump assembly according to claim 1, wherein the separation mechanism includes at least one pre-loaded spring associated with each of the first wear plate and the second wear plate.
 3. The pump assembly according to claim 1, wherein the plurality of wear plates have a first position in which the plurality of wear plates are disengaged from the rotors and a second position in which the plurality of wear plates are engaged against the rotors, the plurality of wear plates being biased towards the first position and moveable from the first position towards the second position.
 4. The pump assembly according to claim 1, wherein the first rotor and the second rotor are formed of a metal material and the plurality of wear plates are formed of a plastic material.
 5. The pump assembly according to claim 1, wherein the rotors are externally toothed gears.
 6. The pump assembly according to claim 1, wherein the rotors are lobe gears each having a plurality of lobes and the housing is a lobe gear pump housing in which the rotors are rotatable without contacting each other.
 7. The pump assembly according to claim 6 further comprising: a centrifugal pump housing attached and fluidly connected to the lobe gear pump housing and having an interior chamber; and an impeller that is arranged within the interior chamber centrifugal pump housing and rotatable within the interior chamber, the impeller being configured to pressurize fluid and direct the fluid to the lobe gear pump housing, wherein the plurality of wear plates axially moves to engage the plurality of lobes when pressure in the lobe gear pump housing exceeds a predetermined pressure threshold.
 8. The pump assembly according to claim 7, further comprising a plurality of wiper inserts, each wiper insert being interconnected to one of the plurality of lobes of each of the first rotor and the second rotor, each wiper insert being depressibly radially biased outward from the lobe of the respective rotor such that the wiper insert can contact the other of the first rotor and the second rotor and the interior chamber of the lobe gear pump housing upon rotation of the first rotor and the second rotor.
 9. The pump assembly according to claim 8, wherein each of the plurality of lobes includes a plurality of wiper retaining recesses, each wiper retaining recess being located at an outermost location of a respective lobe, the respective lobe including a longitudinally extending base and opposing walls extending perpendicularly from the longitudinally extending base to define the wiper retaining recess therebetween for retaining the wiper insert.
 10. The pump assembly according to claim 9, further comprising a plurality of pressure trapping grooves defined in each of the opposing walls of the respective lobe.
 11. The pump assembly according to claim 10, wherein the plurality of pressure trapping grooves includes a first set of pressure trapping grooves defined in a first wall of the opposing walls and a second set of pressure trapping grooves defined in a second wall of the opposing walls, the first set of pressure trapping grooves facing the second set of pressure trapping grooves, wherein the first set and the second set of pressure trapping grooves enable fluid flow out of the wiper retaining recess.
 12. The pump assembly according to claim 10, wherein the pressure trapping grooves are evenly spaced along each of the opposing walls.
 13. A pump assembly comprising: a first rotor and a second rotor that are each rotatable about a longitudinal rotor axis, each rotor having a plurality of lobes that each have a longitudinal lobe axis that is parallel with the rotor axis, the first and second rotor meshing upon rotation without contacting each other; a plurality of wiper retaining recesses defined in each of the plurality of lobes, each lobe including a longitudinally extending base and opposing walls that extend radially outwardly from the longitudinally extending base to define the wiper retaining recess, each of the opposing walls having a plurality of pressure trapping grooves that are defined in the opposing walls and extend radially outwardly for pressure relief in the plurality of wiper retaining recesses; and a plurality of wiper inserts associated with each of the plurality of lobes and retained within the plurality of wiper retaining recesses, each wiper insert being depressibly radially biased outward from the lobe of the rotor such that the wiper can contact the at least one of the other rotor and the interior chamber of the first housing upon rotation of the rotors.
 14. The pump assembly according to claim 13, wherein the plurality of pressure trapping grooves includes a first set of pressure trapping grooves defined in a first wall of the opposing walls and a second set of pressure trapping grooves defined in a second wall of the opposing walls, the first set of pressure trapping grooves facing the second set of pressure trapping grooves, wherein the first set and the second set of pressure trapping grooves enable fluid flow out of the wiper retaining recess.
 15. The pump assembly according to claim 13, wherein the pressure trapping grooves are evenly spaced along each of the opposing walls.
 16. The pump assembly according to claim 13, further comprising at least one wiper spring that biases the wiper insert radially outwardly, the wiper spring being retained within the wiper retaining recess.
 17. The pump assembly according to claim 13, further comprising: a first housing having an interior chamber, the first rotor and the second rotor being rotatable within the interior chamber of the first housing; a second housing attached to the first housing and having an interior chamber, the second housing being fluidly connected to the first housing; and an impeller rotatable within the interior chamber of the second housing.
 18. The pump assembly according to claim 17, further comprising: a first drive shaft, the first rotor being mounted on and coupled to the first drive shaft; a first timing gear mounted on and coupled to the first drive shaft; a second timing gear driven by the first timing gear and mounted on and coupled to a second driven shaft, the second rotor being mounted on and coupled to the second drive shaft; and a drive motor rotatably driving the first shaft in a first direction or a second direction, the impeller being configured to pressurize fluid and direct the fluid to the inlet of the first housing when the drive motor is rotating the first drive shaft in the first direction.
 19. A pump assembly comprising: a drive motor rotatably driving a first drive shaft in a first direction or a second direction; a first timing gear mounted on and coupled to the first drive shaft; a second timing gear driven by the first timing gear and mounted on and coupled to a second driven shaft; a first rotor and a second rotor, each rotor having a plurality of lobes, the first rotor and the second rotor being rotatable without contacting each other, the first rotor being mounted on and coupled to the first drive shaft and the second rotor being mounted on and coupled to the second drive shaft; a lobe gear pump housing having an interior chamber in which the first rotor and second rotor are rotatable; a plurality of wear plates including a first wear plate arranged on a first side of the plurality of lobes and a second wear plate arranged on a second side of the plurality of lobes opposite the first side; and a separation mechanism that is engageable with the plurality of wear plates to enable axial movement of the plurality of wear plates relative to the plurality of lobes, the plurality of wear plates being normally disengaged from the plurality of lobes and axially moveable to engage the plurality of lobes when pressure in the lobe gear pump housing exceeds a predetermined pressure threshold.
 20. The pump assembly according to claim 19, further comprising: a plurality of wiper retaining recesses defined by walls of each of the plurality of lobes, each of the plurality of wiper retaining recesses having a plurality of pressure trapping grooves that are defined in the walls to enable pressure relief within the plurality of wiper retaining recesses; a plurality of wiper inserts associated with each of the plurality of lobes and retained within the plurality of wiper retaining recesses, a centrifugal pump housing attached and fluidly connected to the lobe gear pump housing and having an interior chamber; and an impeller that is arranged within the interior chamber centrifugal pump housing and rotatable within the interior chamber, the impeller being configured to pressurize fluid and direct the fluid to the lobe gear pump housing.
 21. (canceled) 